Connecting the brake resistor allows for quick deceleration because the regenerative power is processed. (The brake torque increases.)
Therefore, when an external brake is used and the inverter coasts to stop, the brake resistor is not necessary.
However, if you are rapidly decelerating the motor from high speed to low speed, the brake resistor may be necessary for this deceleration.
The FR-A500 series with up to 7.5K capacity has a built-in brake resistor.